The present invention relates to controlled release silicone coating compositions. More particularly, the present invention relates to controlled release ultraviolet (UV) radiation-curable epoxyfunctional silicone compositions containing an epoxy-functionalized siloxane resinous copolymer as a controlled release additive.
Silicone compositions are widely used as release coatings for rendering a surface relatively nonadherent to other materials which would normally adhere -closely thereto. Because of their high reactivity, low cost, ease of maintenance, and low potential hazard to industrial users, UV-curable epoxyfunctional silicones are particularly suitable for release applications. UV-curable epoxyfunctional silicone release compositions are known in the art and are described, for example, in U.S. Pat. Nos. 4,547,431 (Eckberg); 4,576,999 (Eckberg); 4,279,717 (Eckberg); 4,421,904 (Eckberg et al.); and 4,952,657 (Riding et al.).
As used herein, the term "release" refers to the force required to separate an adhesive from a surface to which it is adhered. "Controlled release additives" (or "CRAs") are materials added to composition to raise the release of the composition.
Controlled release additives for silicone release coating compositions are known in the art. Reference is made, for example, to U.S. Pat. Nos. 4,123,604 (Sandford, Jr.); 3,527,659 (Keil); 4,547,431 (Eckberg); and 4,952,657 (Riding et al.).
U.S. Pat. Nos. 4,123,604 to Sandford, Jr. and 3,527,659 to Keil, and commonly assigned U.S. application Ser. No. 416,576, filed Sep. 10, 1982, now abandoned, describe MQ and vinyl MQ resinous copolymers as release-increasing controlled release additives for heat-curable silicone release systems.
U.S. Pat. No. 4,547,431 (Eckberg) discloses a controlled release ultraviolet radiation-curable epoxy functional controlled release composition comprising an epoxyfunctional diorganopolysiloxane, a photocatalyst, and an epoxy monomer. The epoxy monomer, in sufficient amounts, functions to raise the release of the cured release composition.
U.S. Pat. No. 4,952,657 to Riding et al. (Riding) discloses the use of a phenolic epoxysilicone copolymer as a controlled release additive for an epoxy functional silicone release coating. The phenolic epoxysilicone copolymer controlled release additive used in the Riding composition provides a maximum release level of only 150-200 g/2 inches.
There is a present need in the marketplace for controlled release additives that can provide release levels of as high as 500 g/2 inches against various pressure sensitive adhesives, such as natural rubbers, acrylics and the like.
Accordingly, the primary object of the present invention is to provide an improved controlled release epoxyfunctional silicone composition having increased release levels, i.e., of at least about 500 g/2 inches.
It is a further object of this invention to provide a method for increasing the release levels of a UV-curable epoxyfunctional silicone composition.
These and other objects are achieved in the present invention.